Continuously variable frictional wheel variators which have at least two torus discs with toroidal races between which roller bodies roll off are known from the prior art. Those frictional wheel variators have a great torque capacity, together with the continuously variable change of ratio.
DE 196 29 213 A1 has disclosed a transmission which can be operated in two power ranges. The essential component parts of said known toroidal transmissions are a continuous frictional wheel variator with two toroidal-shaped races interacting in pairs, one countershaft and one summarizing transmission. A power distribution is provided in the lower (LOW) range. The input power is passed by the input shaft, via a ratio reduction step, to the countershaft and then to the continuously variable transmission (frictional wheel variator) which, on the output side, is connected with the summarizing transmission. Via a second power branch, the input power is passed by the countershaft and a ratio reduction step directly to the summarizing transmission where the power of both power branches is added up and passed on to the output shaft.
In the second power range (HIGH) of this known transmission, the input power is passed, via a ratio reduction step, to the countershaft and then to the continuously variable transmission. One other power portion is not provided in this case.
The Applicant's DE 197 03 544 A1 has disclosed another transmission in which a power distribution is provided and a continuously variable transmission, particularly a transmission with toroidal shaped races interacting in pairs (toroidal transmission), is used. This known transmission also has one intermediate shaft or countershaft to make the desired power distribution possible. In addition, there is provided one planetary transmission with one plus planetary gear set which, depending on power range, either rotates as a unit or serves as summarizing transmission. In the transmission, according to DE 197 03 544 A1, in a first power range, the power is transmitted by the input shaft to the output shaft, via a frictional wheel variator, the planetary transmission rotating as a unit; in the second power range, on one hand, the power is transmitted to the planetary transmission, via the frictional wheel variator and, on the other, directly to the planetary transmission, the power being added up by the planetary transmission and passed to the output shaft.
By the use of a plus planetary gear set, the resulting efficiency of the toothing proves disadvantageous, especially with regard to the efforts of the technical world of offering optimal comfort combined with minimal consumption in the power train.
Departing from the known prior art, the problem on which this invention is based is to outline a transmission which combines the comfort advantages of a continuously variable transmission with an optimized efficiency of the whole transmission and thus with the advantage as to consumption resulting therefrom.